A comment opens after white space, a tab as well as a space, but the plain
scalar terminator checked only for a space before `#`. So `c: d\t#X` kept the
tab and hash as content, giving the value `d\t#X` rather than `d` with a
trailing comment.
Treat a tab before `#` as a space there, in both the lookahead from a white
space character and the check on the accumulated value's last character. A tab
inside a plain scalar with no `#` after it stays content, and a `#` glued to
content with no white space is still content.
Raises yaml-test-suite value-level conformance to 187/194 (96.4%) with the
parse-level and should-error rejection rates unchanged. 448 tests pass.
Mihaela M
6c322fc5ed